Floating tenon size vs mortising bit size

[Gary Grant]

I am attempting my first floating tenon construction on a large dining table. I have a Minimax CU300 horizontal slot mortiser with a 1/2" bit. In making the tenon stock should I plane it to exactly that dimension or perhaps make it a few thousandths thinner?

Obviously I will practice first but any seasoned advice is always welcomed!

THANKS MUCH!!!

[Charles Lent]

Make it a smooth slip fit. If it slides in with just the slightest friction it is about perfect. The glue will tighten it up quickly.

Don't worry about the half round ends of the mortise. Just make the tenons square ended. The sides of the tenon and the quality of fit in the mortise are what gives the joint strength. The half round spaces in the end of the mortise will hold any excess glue. I've used this method for years and never had a failure.

Charley

[David Kumm]

Test the mortise in both end and crossgrain. I have found there can be a slight variation between the two. Have a good flat bottom rasp to touch up the thinner of the two and then friction fit but not too tight dry. Glue will aid in assembly but the tenon should also be run through a saw to slightly groove the sides to avoid the hydraulic lift out and give the glue somewhere to go. Dave

[Prashun Patel]

I don't groove my tenons and have never had an issue with the hydraulic lift. I think it's because there is some gap usually around the ends of the tenons to serve that function?

I bevel the ends of my skinnier (< 3/8") tenons at 45 degrees. On the thicker ones, I bevel the ends less; say 30, and then rasp the shoulders. I don't bevel to a point. Just enough to knock off the corner so the end more or less goes to the end of the slot.

I aim for a fairly tight fit. I prefer if the tenon goes in and comes out by hand with the tiniest bit of effort. I like it to stay put when inserted dry. If it wiggles when I shake the part, I think it's too loose.

I prefer to use a thickness planer when making stock. Table saws and routers tables don't do a good job (for me) at keeping the thickness the exact consistency required to fit a mortise just so.

When/if you use a router table to tweak your ends, use good hold downs. Any little lift will affect your edge treatment.

Regardless of how persnickety I am in making the tenons, I find they very often are a tad tight and require tweaking. To that end, a rasp, and a good block or smooth plane with an appropriate planing stop have been indispensible for me.

Obvious suggestion alert:

Use quatersawn stock.

[lowell holmes]

I've never used the system your using, but I have used slip tenons. If the tenon is snug in the mortise, you may need a place for the glue to migrate to.
If that is the case a groove on the tenon side will relieve the hydraulic pressure. I keep a block plane out to fix the tenons if they are too tight.

I do use mortise pal, but my tenons are shop made.

[glenn bradley]

I also use a Mortise Pal. I groove my tenon stock for tenons over 1-1/2" long but, don't for shorter ones. This just developed with experience. I do follow the advice of the immortal Sam Maloof "leave room for the glue!". If your stock is too tight a couple of swipes with a plane should take care of it.

[Keith Hankins]

Did a ton of floating tenon before the Domino, and I always had it fit snug that i could push in by hand. I left a gap at the bottom for glue, and one side of the tenon light so a slight gap for glue to push out. Also, don't need a gallon of glue. I got to where I judged my joint by not having squeeze out. Never had a failure.

[John TenEyck]

My experience is the same as David's; the mortises in the end grain will be wider than those in the edge grain. I don't think I've ever seen an exception. Therefore, I fit the tenon stock for a smooth sliding fit in the end grain mortises and then use a shoulder plane to adjust the portion that fits in the edge grain for that same smooth, sliding fit. I plane the tenon stock over thickness and then sneak up on the correct fit with my drum sander. Works like a dream. I just finished doing a bunch of 3/4" mortises on my Mini Max FS35 J/P for a table project. The machine did a great job and the joints came together beautifully.

John

[Bill Adamsen]

The axiom quoted here often, "If you can put it together with your hat, it's too loose, if you need a hammer it's too tight."

Loose tenons (slot mortiser or Domino) probably align better than chisel, but I found on a recent job (with chisel) that more time spent on alignment saves considerably on the back end with sanding. I was always happy to grab a door where I had spent a bit more time with fitting. Hand planing with a rabbet plane (or rasp or sandpaper) does give some of that "fit" that always seems to be needed. The above axiom seems to hold pretty true. I like the joint to press together with some force without resorting to a hammer. Gluing up the tenon with a "veneer" is more common than we'd probably care to admit.